1. Field of the Invention
The present invention relates to a network system, and is particularly suitably applied to a PPPoE network system which has plural PPPoE servers and in which connection requests from PPPoE client terminals are distributed among PPPoE servers upon each occurrence of the requests.
2. Description of the Prior Art
PPPoE (PPP over Ethernet) is a client-server protocol proposed to transmit PPP (Point-to-Point Protocol) having been conventionally used for dialup connection and the like via analog telephone lines and ISDN lines over Ethernet (trademark). It is defined by RFC2516 “A method for Transmitting PPP Over Ethernet (PPPoE)” issued in February, 1999 by IETF (The Internet Engineering Task Force). PPPoE is in widespread use as a subscriber holding protocol in broadband access networks such as ADSL and FTTH, and is adopted, for example, in services such as FLET'S ADSL and B FLET'S provided as of November, 2001 by NTT local companies. East Japan Telegraph and Telephone Corporation created “Interface FLET'S Series of IP Communication Network Service—First Edition” in Oct. 17, 2001 as technical reference information on these services.
A PPPoE session establishment sequence (discovery stage) defined in the RFC2516 provides a framework by which, when plural PPPoE servers capable of communicating with PPPoE client terminals exist, the PPPoE client terminals select PPPoE servers of connection destinations.
FIG. 16 shows an example of a message sequence between PC 101 and BASes 132 and 133 when a session is established in conventional PPPoE.
According to the conventional technology, in e.g., PPPoE discovery stage between the PC 101 and BASes 132 and 133, processing comparable to current standard processing such as sequence processing defined in RFC2516 is performed.
The PC 101, which is a PPPoE client terminal, sends a PPPoE Active Discovery Initiation (PADI) message 701 to a broadcast MAC address. The PADI message 701 reaches the BASes 132 and 133, which are PPPoE servers, via a repeater 131, and is received by PADI receiving means 711 and 721. Session management table allocating means 712 and 722 allocate a session management table 643 for managing the sequence and register a Source MAC Address filed 412 in the PADI message 701 in the session management table 643 wherein the Source MAC Address filed 412 stores a MAC address value of the PC 101. The BAS 132 sends a PADO message 703 to the MAC address of PC 101 by a PADO sending means 713, and the Broadband Access Servers (BAS) 133 sends a PPPoE Active Discovery Offer (PADO) message 702 to the MAC address of PC 101 by a PADO sending means 723.
Although the PC 101 receives the two PADO messages 702 and 703, a connection destination selecting means 731 provided in the PC 101 selects either of BASes 132 and 133 to be connected to, according to the value of a service name TAG field contained in the PADO messages. In the example shown in FIG. 16, the PC 101 selects the BAS 133 as a connection destination. In this case, the PC 101 sends the PPPoE Active Discovery Request (PADR) message 704 to the MAC address of BAS 133.
The BAS 133 receives the PADR message 704 by a PADR receiving means 741. A session ID value unique between the PC 101 and the BAS 133 is created by a session ID creating means 742, and is registered in the session management table 643 allocated by the session management table allocating means 722 by a session management table updating means 743. A PADS message 740 with the session ID value set in a ID field 422 is sent to the MAC address of PC 101 by a PPPoE Active Discovery Terminate (PADS) message sending means 744 (the value of the session ID field 422 in the PADI, PADO, and PADR messages is 0x0). In this way, by sending and receiving the PADI, PADO, PADR and PADS messages that shuttle twice, the PPPoE discovery stage is completed between the PC 101 and BAS 133, and a PPPoE session is established.
On the other hand, in the BAS 132 that did not receive the PADR message, a timeout 751 occurs when a predetermined period of time elapses after the PADO message 703 was sent, and the session management table allocated by the session management table allocating means 712 to process the sequence is deallocated by a session management table deallocating means 752.
The establishment of the PPPoE session is followed by PPP negotiation 760. In the PPP negotiation 760, a PPP link is established (LCP), user authentication is made (CHAP or PAP), and an IP address is assigned to the PC 101 (IPCP). Upon completion of the PPP negotiation 760, IP communication 770 is enabled and the PC 101 is connected to the Internet 140.
In the above-described conventional technology by which a connection destination is selected under the initiative of PPPoE clients, access may concentrate on specific PPPoE servers, making it impossible to exploit the full capacity of the PPPoE servers and a network.